"The Future of Energy Storage" webinar: Electrochemical battery technology

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Robert Armstrong: Welcome to this first study of a  series of webinars looking at the future of energy   storage. My name is Bob Armstrong, I'm director of  the MIT Energy Initiative. It's a pleasure to have   this chance to talk to you a little bit about what  we've done on a recent study that we undertook   at MIT looking at the future of energy  storage. This is an interdisciplinary study   at the MIT bringing together faculty  and senior researchers and graduate   students who cover different aspects of energy  storage. If you move to the next slide, Yet.  This is the ninth in a series of this future of  studies, which have the goal of looking at the key   technologies that can play an order of one role  in helping us deal with climate change That is,   technologies that will be important for us to meet  energy needs mid-century, while at the same time   eliminating emissions from the energy system.   This is particularly critical now  as we realize that climate change   is upon us and that we need to move very fast  now if we're to meet objectives that we have. A  

key part of meeting climate change and mitigating  climate change is understood to be decarbonizing   the electricity sector by taking advantage of  renewable energy resources like solar and wind.  As we use those resources in the electricity  sector, we need to understand what it will   take to develop that system in a way that's both  reliable and affordable. Affordability is key,   of course, because, in addition to decarbonizing  the electricity sector, we want, at the same time,   to take that decarbonized electricity and use that  to help us decarbonize other parts of the economy.   Of course, an interesting challenge in moving to  an electricity system that's highly dependent on   variable renewable resources, solar and wind,  is that we need to have storage available   in order that supply and demand  can always be kept in match,   which is a critical part  of the electricity sector.  Key question for the study is, what kinds of  electricity storage technologies kind of policies   would make it possible for us to have this  VRE-dominated electricity system of the future   that's affordable and reliable? All right. Next  slide shows the three main messages of the study.  

Those are, first of all, in the technology area.  What kind of federal R&D policies can we put in   place that will focus on long-duration storage  technologies to support this affordable, reliable   electricity system of the future? Our  second main message is that we can make   net-zero electricity systems affordable  by tailoring storage and mix with variable   renewable resources tailored to different parts  of the country or different parts of the world.  Then, thirdly, we're going to need to take a  relook at market designs and regulatory policies   and reform those to enable equitable and efficient  decarbonization. Those three messages capture   the three main components of the study. Technology  in the first part of the study, systems analysis   in the second part of the study, and then the  third part looked at economics and regulatory   issues. We're going to parallel that set of  main messages in the webinars beginning in   this hour by looking first at technologies. We'll actually spend a couple of the hours of  

the webinar, two hours today and again  tomorrow looking at technologies that we   think can play a role in providing storage  for the electricity system of the future.   Then we'll look at some of the systems  analysis results and then finally turn to   economics and policy changes needed. With  that brief introduction, I'm going to   turn it over to the first two speakers this  morning in this first hour of the webinar. 

Really pleased to have with us Professors Yet-Ming  Chiang from Materials Science and Engineering   and Fikile Brushett from the Department of  Chemical Engineering. They were two members   of a very talented team looking at the  electrochemistry approaches to storage in the   electricity system. Yet, let me turn it to you. Yet-Ming Chiang: Thank you, Bob. Let's see.   Here we go. The message that Bob called out   is this first one, federal R&D policy should focus  on long-duration storage technologies to support   affordable, reliable future electricity  systems. What I want to do in the coming  

slides along with Fikile Brushett is to explain  how we arrive at that takeaway. It involved a   consideration of a broad range of electrochemical  storage technologies. Our approach was to   take a look first at how much storage, grid,  and total storage might be needed globally   by 2030 in near-term, 2050 in the longer term. Based on that estimated total storage,   first what are the materials and supply chain  constraints? We're not going to address that   in this hour, but Elsa Olivetti and Bob Jaffe  will address in the following presentation. What   our group did was to look at electrochemical  storage technologies that could be solutions   and to consider what the manufacturing costs and  other constraints and as well as opportunities   are in arriving at the recommendations  that we present in this study. We will   be capturing really just a snapshot  of the study itself. Our results here  

are represented in a chapter, which is  available for all of the viewers and readers.  The study group for us is the group in  the box on the right-hand side here.   Bob was the chair of the study, I was a co-chair  for this group. The study group was led by Fik   and I. You see the other participants  here. I especially want to point out   or call out the contributions of our student  members here. Well, actually, three of whom have  

now graduated and what you see listed here are  their current affiliations and one Sasha who is   shortly to graduate. Each of these students had  a significant role in the writing of particular   sections of the electrochemical chapter. Now, which electrochemical storage   systems did we consider? There are enormous  diversity of battery chemistries out there.  

It's a certainty that, for instance, your favorite  battery chemistry may not be considered in detail   in our chapter because of the constraints that we  placed on the system to be considered number one,   TRL 6 or greater. You see at the bottom definition  of TRL 6 that the technology has been demonstrated   in some relevant environment. This means that  a full-scale battery has been built and tested.  There are many developing chemistries all the time  historically and today in the battery field, many   of which are promising, but we do not consider  in the study because of this constraint that   we placed on ourselves. The three main categories  we'll talk about today are lithium-ion batteries,  

redox flow batteries, and then metal-air  batteries. The reasons for this will   become apparent. We do also, in the chapter,  consider other batteries. Lead-acid batteries   have been used certainly for grid storage in  the past and also high-temperature batteries.  We'll just direct you to the study  to read in more detail about those.  

Now addressing the point of how much  storage might be needed by mid-century.   The round number that we'll use is 100TWh,  this is arrived at through an analysis that is   pretty granular. It's also supported  by some other estimates that have   recently been published. For instance,  there's a McKenzie study that places the   range of storage needed to decarbonize the  electricity system by 2040 in the range of   80-140TWh. This is just for the electric grid  it does not include electric transportation.   Electrifying the light-duty fleet by 2050  could require another 144TWh, for example.  This target of 100TWh by 2050, is one  of the guideposts in what we did. Now,  

before we get into the details of electrochemical  storage, I want to explain the broader scope of   storage technologies which you'll hear about  in other webinars. This plot on the right   has as its axis the power capacity cost  or power costs, dollars per kilowatt.   Then on the horizontal axis energy  costs, dollars per kilowatt hour.   What you notice here is the grouping of  technologies. Lithium-ion batteries are   typically made with relatively expensive  materials. The storage of energy is costly,   that's the horizontal axis, but it's able  to deliver power at a relatively low cost. 

It turns out that Redox flow batteries are  somewhere in the middle and then Metal-air   batteries as well as the other storage  technologies that you'll hear about in   other webinars, are on the left axis where the  power cost is relatively high, but the energy   costs meaning the materials that are used to  store energy are exceptionally low. One looks   at this and says, "Well, why can't we have it all  and simply be at the origin of this plot?" That's   certainly something we would all love to see, but  it's constrained by physics and chemistry today.   With this let me dive a little bit deeper  and say something about why long duration   and what does long duration mean. Today in much of the storage discussion,   long duration means greater than four hours.  There was a time when greater than two hours was   considered long duration. Here we're really  talking about multi-day gaps in generation  

that need to be bridged, illustrated by this  plot which shows in the black line, the load,   and then the wind in the solar in the blue  and orange colors across all 365 days in 2021.   As you look at this what you see are the gaps  between the renewable generation and the black   line, the load, are gaps that extend over  several days. That's why I say here multi-day   storage. It's not pointing out seasons exactly  and it's certainly more than a day so beyond   the day multiple days of storage is working  definition of long duration will mean here. 

One of the requirements for bridging this gap  is that, well, the competing technology or the   incumbent technology is really natural gas  generation. The next slide I want to present   just a very simple way of looking at what is  required of a storage technology in order to   compete against natural gas on a cost basis.  On the left side of this equation, we have the   lifetime cost of natural gas plant, which  I'll put it there $2,000/kW, and then   if the duration that we're trying to bridge is  multiple days, I'll choose a 100 hours, four days.   What this simple arithmetic tells you is  that the required battery cost, it has to be   $20/kWh or less in order to compete with gas. When we compare that $20/kWh to where lithium-ion   grid storage is today about $250/kWh becomes  apparent why one needs lower-cost batteries for   long-duration storage. With that in mind, and also  noting that this required battery cost is for an   installed system not just, for example, the cell  or even the materials involved. The next plot here  

which appears in our chapter is a way of looking  at the cost of different battery chemistries.   This is just the chemical costs which you see  defined on the left-hand side here. Is the cost   of the cathode, the anode, and the  electrolyte divided by the energy   stored which is the voltage capacity. This  places a floor on the cost of the battery. 

The battery cannot cost any less than  the materials used to store energy.   The vertical axis is a large scale  and the horizontal axis is time, the   date of introduction of that battery chemistry.  On the left axis, you see the pre-1900 chemistries   here. Nickel zinc, lead acid, and zinc air are all  very early chemistries. Then you see approaching   the current date, all these chemistries that  have been introduced. If our goal is to get   below $20/kWh, you see that well we have to start  with something significantly less than 10 and   that really narrows the available options here. We'll talk about these and I'll just even, at this  

point, point out you see that the chemistries that  use a metal or other low-cost inorganic and air   as one of the electrodes for the lowest on this  cost plot. We'll come back to these. Lithium-ion,   the question whether or not lithium-ion given  its incumbent status and can serve all storage   functions is one that comes up often. Recognizing  that lithium-ion battery prices have undergone   this massive cost decline over about three decades  now and that's the plot in the middle here. Back   in 2000, we were above $1,000/kWh. Today we're  down around 100 at the cell level slightly less.  First of all, this cost decline is what has  driven the massive expansion of lithium-ion   in many applications. On the right-hand  side is a plot that shows the manufacturing   capacity of lithium-ion in GWh. The top of  the scale is 2.5TWh. Over the current decade  

2020 to 2030, there is a projected 20% compound  annual growth rate in lithium-ion production,   which at the end of the decade, so this is  primarily driven by electric vehicle demand,   at the end of the decade, we'll be at  2.5TWh of annual production capacity.   When we compare that to the need for 100TWh  by 2050, this implies that the compound annual   growth rate would need to be sustained at  greater than 20% for the next 28 years.  That points out how heavy a lift it is to  do all of grid storage with lithium-ion,   even if the cost continues to decline we find  lithium-ion chemistry is at a lower cost.   Just as a passive in common the lowest  cost lithium-ion storage for the grid   that's on the horizon today is going to be  lithium-ion phosphate based for several reasons,   including cost and the material supply. Even in  that case, however, the growth of production will   need to be massive and sustained. This illustrates  why we might want to look for alternative  

chemistries. This plot is just a more granular  look at the lithium-ion cell in this context   and the stack bar chart here are all the cost  components that go into a lithium-ion cell.  The different vertical bars represent  different lithium-ion chemistries   from NCA, or nickel cobalt aluminum cathode  to LFP, lithium iron phosphate cathode,   and highlighting the parts of the bar are the  electrolyte, anode, and cathode. If you add   those up, you'll see that these all cases exceed  $20/kWh, which was that long-duration cost target.  

That illustrates some of the constraints of  lithium-ion for multiday storage. The other one,   which I'm only going to mention briefly here  because the next hour we'll discuss this in much   greater detail. These are results from the part of  our chapter that Elsa already and Bob Jaffe led.  This table shows you four of the elements  that we would consider strategic to   one case, lithium-ion chemistry and then  vanadium, related vanadium redox batteries, which   Fikile Brushett will talk about next. The  third column over is the CAGR to reach 100TWh  

by 2050. Highlighted in red  are those cases where the   CAGR and new growth rate needs to be greater than  the historical CAGR, which is the first column,   the column to the left. Then compare against  that in the last column is the resource limit   and highlighted in red there  are cases where the resource   limit may not allow you to reach 100TWh by 2050. This highlights the following point that it's in   several of these cases, not the resource limit,  not whether or not you have enough of that metal,   but what the production of that metal needs to  be in order to reach these storage targets by   mid-century. Here, you see that, well, in the case  of lithium, it's actually not the resource limit,   but the fact that the production needs to  be sustained at this very high level even   though historically, there have been instances  where lithium production has reached that level.   Cobalt nickel vanadium, you see that you have  to exceed the historical production increases in   order to get there and you have to sustain those. This is the end of my discussion about lithium-ion  

for grid storage. We believe that it  will continue to be very widely used   for short-duration storage, but the other  chemistries will need to be developed for   long-duration storage. With that, I'm going to now  pass the mic as it were over to Fikile Brushett   who will now tell you about redox flow batteries,  and then I'll come back at the end and say more   about metal-air batteries. Fikile, over to you. Fikile Brushett: Thank you, Yet. Good morning,   everybody, at least this morning for me. I'm glad  to be able to speak with you a little bit about   maybe what might be some of the technologies  that will complement lithium-ion batteries and   will be useful for long-duration energy storage. I  wanted to talk a little bit today about redox flow   batteries. Yet, I'm going to have to ask you  to click through a couple of animations here.  

A redox flow battery essentially consists of  tanks of solubilized energy storage material   that are pumped through a reactor where  they are charged and discharged. Yet,   maybe if you could click to the next animation.  Within the tanks, there is an active species   that is dissolved in an electrolyte. The electrolyte, it can be something  

like sulfuric acid and water. What you rely  upon is the fact that the active species in   each of these tanks have redox potentials that  are different from one another. These disparate   redox potentials gives you then the cell voltage.  Yet, maybe you could click forward one more time.  

This allows you to charge and to discharge  the battery. One more click, Yet.   Where are the reactions actually occur is in an  electrochemical reactor. Yet, maybe click one   more time, which is very similar to a fuel cell,  a low-temperature fuel cell for those people   who are familiar and essentially involves flow  fields, carbon paper electrodes, and a membrane.  The membrane, Yet click one more time, is  particularly important here because it keeps   the electrolytes apart from one another.  What you want the membrane to do, Yet,   click one more time is to allow ions to move back  and forth between the two electrolytes to balance   charge as the electrons move through the external  circuit, but you want the membrane to block active   species from going back and forth across. Yet,  maybe click one more time. You want it to block   the active species from going across, but allow  ions to move through. You need permselectivity.  

Abutted to that membrane or electrodes  so-- Yet, if you could click one more time,   and within these porous electrodes is  where the electrochemical reactions occur.  The active species is brought to these  porous electrodes through engineered   flow fields. The example that I'm showing  you here is an interdigitated flow field,   where the lighter blue areas are open channels  and the darker areas are ribs. If you look at now   the picture on the side there, those ribs  then force the electrolyte through the porous   electrode, where the electrochemical reactions  will occur. Maybe, Yet, click one more time.  

This force convection through these porous  electrodes that are things like carbon paper   lead to the redox reactions that occur  on the surface of the porous electrode,   and then the material will move out of  the reactor and move back to the tank.  Essentially, you're cycling these materials around  and around to charge and discharge them when you   want to store energy or when you want to release  energy to the grid. Click, Yet, one more time.   The potential benefit of this particular  architecture for longer-duration energy storage   is the decoupling of power and energy scaling.  The energy is proportional to the tank size,   or the number of tanks that you have. The  power is proportional to the reactor size,   or the number of reactors that you might have.  You can independently specify these things and   once you have an installation, it is possible  to change these things independently to meet   changing or emerging needs. The second  is relatively simple manufacturing. 

You're talking about mixing electrolytes,  dissolving active species in acids or other sorts   of electrolytes, and storing them in tanks. Then  the reactors are relatively simple manufacturing,   don't require clean rooms to do the assembly.  They are relatively durable depending upon the   active material. I'm going to come back to this,  and require relatively low-cost maintenance.   By the durability, what I mean is that the active  materials are reacting on the surface of the   electrode. There's no intercalation reaction,  which could lead to materials decay. As long as   your active materials are relatively stable, this  system can run for a very long period of time.  Then finally, there's relative location  independence as compared to other long-duration   potential storage systems such as pumped hydro  storage or compressed air, or things of that   nature. However, there's no free lunch and that's  what this last click is here for. You're losing  

energy density when you have a system like  this as compared to lithium-ion because your   active materials are dissolved in electrolyte and  stored in external tanks rather than a compact   cell as you'd have for a lithium-ion  type battery. For this particular system,   it looks more and more attractive, the longer  and longer duration energy storage you have.  As the tanks get larger, and the reactor gets  smaller, you're asymptotically approaching the   cost of the materials in the tank, the reactor  becomes a smaller and smaller component. That  

energy cost gets lower and lower until you get to  the materials in the tank. If we go to the next   slide, you might ask yourself, "Well, what's  in the tank?" Vanadium redox flow batteries   would be the state-of-the-art technology  today. This slide shows the vanadium redox   flow battery. If you look on the far left-hand  side, you can see a simple diagram of the cell.   What I want you to take away from this is that  you have vanadium on both sides of the membrane.  You're taking advantage of the fact that vanadium  has four stable and soluble redox states within   an aqueous water window, in this case, sulfuric  acid. You have vanadium 23 on the negative side,   the more negative side, and vanadium 45 on  the more positive side. This is particularly  

advantageous because the ion-selective  membranes are not perfectly ion-selective.   It's possible over long duration operation that  some vanadium ions are going to move across   that membrane and interact with the species  on the wrong electrolyte. If you have all of   the same species on either side, though, you're  based upon the same parent compound rebalancing   or resetting the system simply involves moving  solution from one tank to the other periodically.  This means that the system can be very durable and  can run for a long period of time. Once it gets  

out of balance, we can put it back into balance  by shifting the electrolyte around. The second   aspect here is that vanadium does not decay during  operation. It does not turn into another species   and so it can be recovered at the end of life  and resold or replenished or it can be recycled.   This also opens up opportunities for different  economic models like electrolyte leasing, where   you might lease the electrolyte from a company  and the company might take it back after a while   at the end of life or other types of recovery and  re-utilization strategies towards the end of life.  Vanadium flow batteries have been around  since the 1980s. I think they were first  

proposed by Professor Maria Skyllas-Kazacos, and  have led to a number of companies working on them   for many years. The example that I show in the  middle is from Sumitomo Electric Company in Japan,   but there's also companies in the United  States, Largo Clean Energy in Massachusetts,   and in Europe. The disadvantages of this  particular system are the high cost of vanadium.   Vanadium right now is quite expensive. You'll hear  a little bit more about that in the next hour.  

At least, initially, right now, these  technologies are quite expensive as   compared to lithium-ion batteries which  hampers their ability to be deployed.  In the long run, if we were thinking about using  vanadium and we wanted to scale up and try to   reduce the costs, what we might find is that we  may run out of vanadium when we get to a certain   amount of deployment. As we begin to think about  these new technologies, the vanadium flow battery   might carry us some of the way in terms of the  flow battery technology, but it may not carry us   all the way to multiple terawatt type deployment,  and you'll much more about that coming up.   If not vanadium, then what? If we go to the  next slide, we might then think about, well,   what electrolytes could we begin to think  about using that are not vanadium related.  What you find is that it's actually  quite challenging to identify   electrolytes that meet all of the criteria needed  for low-cost efficient energy storage. We need   to identify materials that have favorable redox  potentials, those are the electrode reactions that   are associated with the cell voltage, you want  that to be high. You want the reaction kinetics  

to be fast. You want them to be soluble in common  electrolytes. You want them to be conductive and   to work favorably with membranes. You don't want  them to go across. They have to be inexpensive   and they have to be safe. The point of this  slide is simply to say that there are always  

going to be trade-offs and compromises  as you think about these new materials.  Yet, if you go to the next click, there's always  a trade-off for our compromise. As we begin to   look for new materials, we want to look for  effective property sets that allow us to get to   low-cost safe energy storage. The last slide for  me is the next slide to say, where are we going?   There are two clear pathways that I can see  towards lower-cost redox flow batteries. The   first is on the left-hand side here is commodity  scale inorganic materials, things like sulfur,   iron. Materials that are abundant that have  a materials production infrastructure ready,  

and they may actually be used at the  waste products that could be reused or   recycled for long-duration energy storage. The challenge with an approach like this is   the upgrading requirements, taking a material  that's a waste product and converting it into   an electrochemical product that might take some  effort. There are also technical attributes that   we need to be concerned about. These materials  can't really be modified so they're going to  

have a set efficiency and a set electrochemical  reversibility that we'll need to work around,   and this may lead to increasing cost in other  system components that would be needed in   order to realize these inexpensive energy  storage systems. The second approach is to   the right-hand side of the slide and that's  engineered molecules via organic chemistry.  The idea is, can we take organic molecules,  aromatics let's say potentially from   petrochemicals or from other feedstocks, and  modify them through molecular functionalization to   make them energy storage materials? This approach  could be quite attractive because it would enable   you to have tunable technical properties depending  upon how you modify those reactive cores. They're   based upon relatively abundant constituent  elements and have the potential for mass   production, at least for some of the targets, if  we rely on ongoing organic materials production.  

The challenge that those materials face is  molecular stability. Can they last for as   long as you need for long-duration energy  storage in order to recoup your investment?  There's potential cost and scalability  challenges as the desired high-performing targets   don't often match those materials that can  be scaled at low cost. Identifying that   nexus where we have materials to perform well  enough to form long-duration energy storage,   but are also cheap enough to be manufactured  at scale is where we need to look for these   types of materials. With that, I thank you for  your attention. I'll be around for questions,   but I wanted to pass it back to Yet. Yet-Ming: Thanks, Fikile. Let me   now move to this third type of battery that we  referred to earlier which is metal-air batteries.  

Again, I'm showing this plot again  just to show you down at the bottom,   but what are our options in the area of metal-air  batteries, and you see aluminum-air, iron-air,   lithium-air. We won't talk about lithium  or even really aluminum very much, but   let me give you now an idea of what a  metal-air battery is and what the issues are,   what the advantages are, and why we think it's a  category that has promised long duration storage.   It turns out that almost any metal you can  oxidize, you can make into a metal-air battery. 

Especially, if it's a primary  or disposable metal-air battery,   and the zinc-air battery for hearing aids is the  most common example. That is a battery where you,   in the oxidation of zinc, you see the small  image on the upper right here shows how this   functions. You oxidize the metal, in the process  you draw electrons, and then you produce an   oxide or hydroxide which is a reaction product,  and that then is how you discharge the battery.   At the end of that process, you can throw it  away or recycle it, but very few metal air   chemistries are rechargeable. Lithium,  zinc, and iron are the ones that have   been demonstrated to be rechargeable although  there are efforts to make others rechargeable. 

In the periodic table here, you see some of the  examples and also some of the companies who have   worked on commercializing metal-air battery  technology. Lithium-air has been primarily studied   as a very high energy density battery chemistry  for transportation reasons or applications.   Rechargeable zinc-air has been studied by several  companies and is one of the low-cost metals that   one could conceivably use for rechargeable  batteries for grid storage. There are ongoing  

efforts as well as past efforts and in cases  where thousands of batteries have been deployed   in the field. The iron-air battery I'll spend  more time on in the coming slides was originally   studied by Westinghouse back in the 1960s. More recently, a company that I'm associated with,   Form Energy has picked up on this chemistry and  is developing iron-air batteries for grid storage.  

Then finally, I'll mention that even carbon  is something that can be oxidized. The carbon   air battery is something that a company,  Noon Energy, is working on commercializing.   You see that there's a range of these, but  not a very wide range. There are some clear  

issues with metal-air batteries. One of the  ones I'll point out right here is the fact   that the round trip efficiencies are relatively  low, but whereas a lithium-ion battery might   have a round trip efficiency at low current  rates of greater than 90%, here we're really   talking about 40% to 60% route of proficiencies. Also, the balance of plant costs here that you   require an air electrode, you require the supply  of air, that you require management features that   you don't need in the case of lithium-ion  battery, so BOP costs tend to be higher.   Now, the iron-air battery is one that, so using  this as an example, this is one we might call   just a reversible rustic of metallic iron. These  two images show what happens during discharge  

on the left-hand side. Discharge for a battery  is always what is spontaneously downhill from an   energy point of view. Energetically downhill,  the iron wants to rust. The oxidation forming   iron hydroxide is the discharge process, and  the iron hydroxide is the discharge product. 

The charge process simply refers to  electrically recharging that battery,   sorry unrusting that battery, and that's  illustrated on the right. This can be done in an   aqueous electrolyte environment using an alkaline  electrolyte, which is relatively low cost.   Now, it turns out that most versions of iron-air  batteries actually use two air electrodes. If you   think of the air electrode as the lung, this  is an instance in which you have actually two   sets of lungs, one for inhaling, one for  exhaling. The air electrode for taking in   oxygen, the oxygen reduction process, and making  that oxygen available to the iron for oxidation,   is referred to as the gas defusion electrode, or  the ORR electrode, Oxygen Reduction Electrode.  Then there's actually an evolution electrode which  is the generation of oxygen gas that leaves the   system. Then you have the third electrode which  is metal anode. You see the reactions down here  

at the bottom for the iron air case and on the  right is an example of a charge-discharge process.   No battery is perfect, all batteries have their  flaws, and I pointed out the roundtrip efficiency.   Let me explain just a little bit more detail where  that comes from. The charge process you see here   on the horizontal axis is the capacity. You see  that in charging the battery more electrons go in,   there's a higher charge capacity than discharge  capacity. This is called a coulombic inefficiency.  In this case, this comes from the fact that at  the iron electrode the potential is very close   to the hydrogen evolution potential for  this system. You put some of the electrons  

in charging into the generation of hydrogen,  so that needs to be managed and that's one of   the reasons for the round trip inefficiency,  the coulombic inefficiency. The second is the   gap you see on the voltage scale, the vertical  scale between charge and discharge and that's a   voltage inefficiency and that's primarily due to  over potentials necessary at the air electrode.   You see the limitations of the iron air battery,  it's not a very good battery for a high-power   rapid charge, rapid discharge scenario, not  good for an electric vehicle, for example,   but the very low cost is what makes it compelling. In designing an iron air battery for grid   storage the question is whether or not  they're very low cost, that advantage   overcomes the other limitations.  From a supply chain perspective,  

iron is very interesting and what I show here is  an image of the different states of iron as one   goes from Iron Ore which is iron oxide, which  is then pelletized. What I've outlined in the   box in the middle here is the first stage in this  iron supply chain where you have metallic iron.   It's a material called Direct Reduced  Iron or DRI which is actually some 95%   metallic. At this stage, that iron oxide or  iron ore has become reduced in this pellet form.  This industry exists primarily to feed the  electric arc furnace industry. To the right  

you see some other forms of iron but the iron  ore pellets here, DRI are used to feed EAF,   Electric Arc Furnaces, which are a cleaner form  of iron production and steel production-- I meant   steel production, then the blast furnaces of the  past. This is what Direct Reduced Iron looks like   in volume. Here's a drum full of these pellets.  On the right-hand side is an example of what a   iron air battery, this is about 4 feet  tall, 4 feet wide about a foot thick.  

This is what a large-scale battery certainly,  large scale compared to let's say your lead   acid battery or your lithium-ion  battery, what that might look like.  There really is no supply chain limitation made  here. These two images show the structure that   you see is a vertical shaft furnace and there's  a conveyor that brings the iron ore pellets to   the top and over days they work their way down  through this vertical shaft furnace and emerges   that DRI that I showed you. On the left-hand  side what you see those mounds in front of the  

shaft furnace are big piles of iron ore pellets  waiting to go through the shaft furnace.   The numbers you see in the text here. If we were  to reach a 100TWh even over just 10 years, it   requires less than a 10% increase in global iron  production and that's because there's such a large   industry already in place for steel production. There's a supply chain in the US, there's a   domestic supply chain as well as on every other  continent on the planet. This is some of the   reasons why low-cost metal-air, we believe, is  one of the ways of meeting that less than $20/kWh   greater than a 100TWh demand that might be  required to decarbonize electricity system   by 2050. Before I close with just some takeaways.  I wanted to just show here in this slide   some of the other technologies that you'll  hear about, you've heard here about redox   flow batteries of metal-air as well  as lithium-ion. You will hear about  

thermal energy storage in another presentation and  also you'll hear about mechanical energy storage.  There are some highlights here about what  you'll hear about there. Very briefly   in the thermal storage case, you'll hear about the  challenge of heat to electricity and a particular   approach that's been identified as low cost and  relatively near-term. Which is to take existing  

power plants, which already have the heat to  electricity, and applying to the front end a   thermal storage option for producing the steam.  That is our collective view, the authors of this   study an attractive option. You'll hear about  mechanical energy storage, which is continuing   to grow in other parts of the country, but it's  really constrained in the US and elsewhere.  

With that let me just close with this slide.  Which is takeaways on electrochemical storage.  Electrochemical technologies are the highest  energy densities that storage technology that   we have except for chemical energy storage.  By that we mean hydrogen and that also it   will be addressed in another presentation. On a  power per area basis, these are attractive. The   battery systems are typically relatively simple in  their design, and they can be scaled. They can be   applied at smaller scale as well as a larger  scale. They scale down well there are a lot   of storage technologies that do not scale down  well. Just for something like residential storage,  

for example, they would be more attractive. We  discussed lithium-ion batteries. There is no   apparent successor to lithium-ion in  electric vehicle transportation today.  Also, for short duration  storage for the electric grid,   today 4 hours or less in the future that may be  8 or 10 hours or less as the costs come down.   We believe that they'll continue to be used in  these short-duration grid storage applications.  

One of the things that's benefited  the deployment of lithium-ion for grid   storage is the fact that they're used other  applications, especially electric vehicles.   The other technologies we've talked about  redox flow management and metal-air do not   have the benefit of drafting on another very  large application such as electric vehicles.   That's in some ways a constraint. However, the critical materials that need to   be produced to take lithium-ion to a very large  scale are running into supply constraints and   you'll hear about that in the next presentation.  This is why we end up with the main takeaway,  

that for long-duration storage which we see is  necessary. DOE as one agency should be supporting   R&D and demonstration to advance longer duration  technologies that rely on earth-abundant   materials. With that, let me stop. I think we have  about five minutes left for Q&A. I know that there   have been a very large number of questions  I see that have floated in as we've talked   here. I'm going to stop sharing and let's see. Robert: Okay let me, put some questions to you,  

Yet and Fikile. Before I do that, let me  just point out to the audience if you would   type in any questions into the Q&A  button at the bottom of your Zoom screen.   We'll try to get this many of these as we  can. Secondly, a question that came up is   with the recording of this be available  and the answer is yes. We will send out   a link to the recording in about two weeks as soon  as we get it processed so that will be available.   Let me start. One of the questions that came up,  Yet and Fikile, is a question about the relative  

lifetimes of these different chemistries. If you  could speak to cycle life or over a lifetime.  Yet-Ming: I'll just jump in. Fikile, can of course  add. One things about long duration storage is   that if you think about installations as being  utility-scale and roughly 20 years of lifetime,   the longer the duration the fewer  the cycles you actually need.   In some cases, in development of technology,  recently there's been an emphasis on having many,   many cycles, and then you realize that actually,  you don't need that many cycles if you're doing   multi-day storage and these full cycles. We can all do the arithmetic, and so the   many thousand cycles that you're doing daily  cycling over 10 or 20 years, but as you go to   multi-day storage, over the entire lifetime  of multi-day storage system, you might only   see a few hundred cycles. That's actually a  benefit for technology development. Fikile,   perhaps you can say something about  cycle life and calendar life for RFPs. 

Fikile: Thanks, Yet. I agree with everything you  said. The subtle difference to this question would   be the type of decay mechanism that  is impacting the battery. There are   cycle-dependent decay mechanisms and  there are time-dependent decay mechanisms.   For cycle-dependent decay mechanisms, if you're  not cycling as much, then it won't decay as much.  

For time-dependent mechanisms, the more time  you operate, it will decay more. In the case of   flow batteries, just to put an example  there, for many of the advanced organic   or organic metallic or metal-centered coordination  complex chemistries, their decay rates are   dependent upon time rather than cycle rates. A big challenge in that area is identifying   materials that are stable enough to either  last for the duration of the installation   or materials that are stable enough that periodic  replacement becomes economically viable. Those are   some of the things that we think about when  we think about long-duration energy storage,   at least within flow batteries. Robert: Thank you. One of the questions   that came up, I'll just ask Kelly to provide  a link to the future of energy storage study.   Someone asked for a link to the report that Yet  referred to. We'll send that out to the registered  

attendees. Second question refers to  the footprint, so not the cycle life,   but the footprint of the different battery  technologies, how much space do you take up,   and does that impact where you might be able to  use these batteries? For example, metal-air or   redox flow batteries versus lithium-ion  batteries, if you're trying to go that route.  Yet-Ming: In comparison to lithium-ion batteries,  lithium-ion batteries are very energy dense.  

Both RFPs in metal-air batteries,  they will take a more footprint,   but compared to other storage technologies, they  are still very energy-dense and very compact.   For example, metal-air batteries their  typical energy density fill the installation   counting all of the balance of plant, would  have a power per acre, which is roughly   that of a natural gas power plant. That's  a number of 1 to 2 megawatts per acre.   In the context of the acreage required for wind  or solar generation, that's going to be small.   Unlike, for example, pumped hydro in which the  footprint, of course, is going to be very large,   for the same amount of power. Robert: Let me ask a very specific   question about the solid-state batteries,  question came up, what about those?  Yet-Ming: That's a good question. Today, most  of the emphasis has been on high energy density  

and also high-value applications such as  electric vehicles, high-value applications   for solid-state batteries. That's where  most of the R&D is. If the cost is there,   grid storage would absolutely would make sense.  I wouldn't rule it out, but I think I would   put it in a similar category as lithium-ion  today as being value for high energy density.   At this point, at least not having yet  demonstrated the kind of cost trajectory or the   ability to use low-cost materials that would  make it attractive for longer duration. This   is coming from someone who spends a lot  of time working on solid-state batteries. 

Robert: Maybe one last question in this  section. A number of people asked about these   sodium-ion batteries and sodium-ion chemistry. Yet-Ming: I saw one of those questions. It is not   yet at TRL6, it's one of the reasons we didn't  include it. I think the short answer is that,   yes, moving to sodium-ion for lithium-ion, there's  a trade-off there in energy density and so the   voltage of sodium-ion is typically less than that  of lithium-ion. It's not a direct reduction in  

costs just by substituting for lithium, but  it certainly would help solve the lithium   supply chain question. The manufacturing  scale-up is similar, there still is a   manufacturing constraint. Sodium-ion,  I think, it's on the horizon. You'll   just need sodium-ion gigafactories,  instead of lithium-ion gigafactories.  Robert: Fikile, any comments? Fikile:   Yet said it well. Robert: Okay. Good.   There are a lot of other good questions, some on  environmental impacts and so on-- I think we'll   bring those up during the next section where  we talk about materials, but it's out to a   great start. Thank you very much Yet and Fikile  for those comments and answers to questions.

2022-08-08 23:41

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